1. Field of the Invention
The present invention relates to electrostatographic imaging and recording apparatus, and particularly to assemblies in these apparatus for fixing toner to the substrates.
2. Description of Background and Other Information
Generally in electrostatographic reproduction, the original to be copied is rendered in the form of a latent electrostatic image on a photosensitive member. This latent image is made visible by the application of electrically charged toner.
The toner thusly forming the image is transferred to a substrate, such as paper or transparent film, and fixed or fused to the substrate. The fusing of toner to substrate can be effected by applying heat, preferably at a temperature of about 90xc2x0 C.-200xc2x0 C.; pressure may be employed in conjunction with the heat.
A system or assembly for providing the requisite heat and pressure customarily includes a fuser member and a support member. The heat energy employed in the fusing process generally is transmitted to toner on the substrate by the fuser member. Specifically, the fuser member is heated; to transfer heat energy to toner situated on a surface of the substrate, the fuser member contacts this toner, and correspondingly also can contact this surface of the substrate itself. The support member contacts an opposing surface of the substrate. Accordingly, the substrate can be situated between the fuser and support members, so that these members can act together on the substrate to provide the requisite pressure in the fusing process.
During the fusing process toner can be offset from the substrate to the fuser member. Toner thusly transferred to the fuser member in turn may be passed on to other members in the electrostatographic apparatus, or to subsequent substrates subjected to fusing.
Toner on the fusing member therefore can interfere with the operation of the electrostatographic apparatus and with the quality of the ultimate product of the electrostatographic process. This offset toner is accordingly regarded as contamination of the fuser member, and preventing or at least minimizing this contamination is a desirable objective.
Release agents can be applied to fusing members during the fusing process, to combat toner offset. Further, fusing member surface layers can incorporate fillers for the purpose of strengthening the bonding of release agents to these surface layers, and thereby improving release properties.
U.S. Pat Nos. 4,257,699, 4,264,181, and 4,272,179 each discloses an exhaustive number of metals, metal alloys, metal salts, and metal oxides, including iron oxide, for use as fuser member surface layer fillers; these same patents also list hydroxy, epoxy, carboxy, amino, isocyanate, and mercapto functional polyorganosiloxanes all as being suitable release agents. U.S. Pat. No. 6,011,946 discusses the importance of employing the correct combination of surface layer material, filler, and release agent; this patent is directed to a fuser member with a polymeric outer layer including a zinc compound dispersed therein, and a specified aminofunctional polyorganosiloxane release agent overlaying this outer layer.
It has been discovered that the particular combination of release agents comprising aminofunctional polyorganosiloxane, used with fluoroelastomer fusing surface layers with ferric oxide filler, provides unexpectedly superior results, with respect to features such as resistance against toner offset and release activity. Fusing surface layers incorporating Fe2O3 have been found to exhibit a surprisingly high degree of interaction with the aminofunctional release agents as indicated, thereby enhancing the thickness of the protective layer that these release agents form on the fusing surface.
The assembly, or system, of the invention includes a fuser member. The fuser member comprises a fuser base and an overlaying fusing surface layer. The fusing surface layer comprises a fluoroelastomer and contains Fe2O3 particles. It can reside directly on the fuser base, or a cushion and/or other material can be interposed between the fuser base and the fusing surface layer.
The fuser member, or at least the fusing surface layer, is heated, thereby providing the requisite heat energy for the fusing process. A release agent comprising an aminofunctional polyorganosiloxane, preferably in the form of a fluid and most preferably an oil, is applied to the fusing surface layer. This layer contacts toner on a substrate to effect fusing of the toner to the substrate, and can further contact the substrate surface on which the toner resides.
A support member for cooperating with the fuser member can be employed. During the fusing process the substrate is positioned between the fuser member and the substrate, and they cooperate to exert pressure on the substrate. The fuser member and the substrate define a nip that the substrate passes through, thereby providing appropriate pressure for the fusing process.